1. Field of the Invention
The present invention relates to an oil filter to be incorporated in a lubricating system for an internal combustion engine or the like and, more particularly, to an improvement in an oil filter of the type which can remove not only solid contaminants but also gaseous contaminants from the oil.
2. Description of the Prior Art
In machinery for construction, transportation and the like using lubricant, such as engines and various hydraulic devices, solid contaminants and gaseous contaminants have hitherto been removed from lubricant by separate devices and/or in different portions of the machinery. An integrated device has thus been desired which can remove both of the solid and gaseous contaminants effectively and which can be installed in a limited space of the machinery.
The inventors herein have proposed such an integrated device which is disclosed in a U.S. Pat. No. 4,865,632 owned by Mitsubishi Oil Co., Ltd. and issued Sep. 12, 1989. The device comprises a first separator for filtering lubricant which is pumped into a housing to thereby remove solid contaminants, and a second separator for removing gaseous contaminants from the filtered oil by utilizing a centrifugal force. Specifically, the second separator has a chamber adapted to generate a vortical flow of the lubricant introduced therein, whereby the lubricant having little gaseous contaminants and therefore having a larger specific gravity gathers in a peripheral area of the chamber while gas-rich lubricant having a smaller specific gravity gathers in a central area. A funnel-shaped wall defining the chamber and converged toward the lower end is provided with a plurality of pores through which the gas-removed lubricant flows out of the chamber. On the other hand, the gas-rich lubricant is discharged by a pipe which extends into the chamber along its axis and has a plurality of orifices formed in the substantially whole portion within the chamber.
In the above proposed device, gas-containing lubricant is introduced tangentially into the chamber at the upper cylindrical portion of the funnel-shaped wall, and the gaseous contaminants are instantaneously collected around the upper portion of the pipe. Since a diameter of the chamber becomes smaller toward the lower end with reducing a distance between the funnel-shaped wall and the pipe, the lubricant containing little gaseous contaminants approaches the pipe at the lower portion thereof and flows into the pipe through the orifices to mix with the pre-removed gas-rich lubricant. Thus, separation of the gaseous contaminants in the above proposed device is still considered unsatisfactory for practical use.